Central nervous system infusions of propionic acid (PPA) a metabolic end product of enteric bacteria, particularly those associated with some forms of autism spectrum disorder, produce reversible hyperactive and repetitive behavior (top right) in rats, compared to phosphate buffered saline (PBS) vehicle infused control rat (top left). Pairs of control rats infused with PBS vehicle display normal social behaviour (bottom left), compaired to pairs of rats infused with PPA, which show markedly reduced social interaction (bottom right). PPA infused rodents also display object fixation, tics, seizure disorder, and brain neuroinflammatory, oxidative stress and lipid profiles consistent with those found in patients with autism spectrum disorders.